Consumers and users of mobile wireless devices are increasingly demanding and using broadband data services. For example, mobile wireless devices are often designed and configured to receive video, audio, and multimedia content, and are typically equipped with high quality video and audio output devices. In one example of a broadband application, many mobile wireless devices are arranged to receive the same live video and audio signal. In this way, the video and audio signal is “broadcast” to many mobile users, and each of the mobile devices receives and presents the video and audio to its respective user.
The use of a broadcast process enables a more efficient use of the network's forward communication link, that is, the communication link from the base station to the mobile devices. Since communication bandwidth is a limited resource, the broadcast model is particularly desirable. Because transmission quality is constantly changing in a wireless network, it is likely that at least some of the mobile stations in a coverage area will fail to receive some of the broadcast packets. Accordingly, the typical broadcast transmission system queries its mobile stations to determine channel quality for the worst user in the broadcast reception area, and the broadcast transmission scheme is then set according to the worst user's channel conditions. By determining and presetting the transmission scheme to the worst expected conditions, the broadcast is likely to be received by at least most of the intended mobile units. Unfortunately, because the selected modulation, power, and coding is set for the worst user, the overall efficiency and capacity for the network is reduced. Since transmission conditions change over time, a predetermined transmission scheme is unable to appropriately adapt to changing broadcast needs.
To provide adaptability, the network may require that mobile units provide an acknowledgment that broadcast packets have been successfully received. In this arrangement, the network sends data packets to each mobile unit, and the mobile unit responds to the network with an acknowledgment (“ACK”) response. By acknowledging receipt of the data packets, the network can be assured that mobile stations are properly receiving data. For those mobile stations that do not respond with an ACK, the network resends the “lost” data packets until the mobile can acknowledge receipt. Unfortunately, the mobile devices send their respective ACK responses on the reverse link, that is, the communication link from the mobile device to the network. Typically, the reverse link has much less robustness compared to the forward link, and therefore is subject to overloading or other detrimental effects due to the transmission of many ACK signals from the mobile devices. In some cases, a network operating in a broadcast mode may be sending the same data packets to hundreds of mobile devices, and all the mobile devices may be attempting to send an ACK at about the same time. Since the reverse link may overload, or least cause a delayed response, the network may assume that many of the mobile devices failed to receive the broadcast, and begin resending data packets to many of the mobile devices unnecessarily, thereby causing stress and/or overload to the network, and degrading the quality of broadcast service. In some cases, such conditions may even cause failure of the network system.
As an alternative to waiting for an ACK response, a network may be configure to count a no-acknowledgment (“NACK”) response that indicates that a mobile station did not successfully receive a complete set of data packets. In this way, a mobile device may begin receiving a set of data packets, and if all packets are received, not send any ACK or NACK response. However, if not all the packets are received, then the mobile device requests that the packets be resent by transmitting a NACK message to the network. The network, upon receiving the NACK, may resend the data packets to the mobile device. Although this arrangement causes less congestion on the reverse link, substantial “resend” traffic is generated on the forward link. In one particular problem, there may be some mobile devices on the fringe of the network, or positioned for poor transmission quality, which cause a continual resending of data packets. In this way, the network continues to use the forward link to send large amounts of data to the “fringe” mobile devices, with only a limited chance that these “fringe” devices will actually receive and decode the received data in a timely manner. In a similar manner, these same “fringe” devices continually generate and send NACK messages on the reverse link, which, due to the unreliable communication link, may or may not be received by the network system. In this way, the network expends an undue bandwidth on a few devices, and these devices have little chance of successfully presenting the broadcast data.
Because of the undesirable effects for providing broadcast feedback, most broadcast systems currently preset a “worst case” transmission scheme, and blindly use that scheme to broadcast content data to its remote devices. Accordingly, there exists a need for a more efficient and effective system and method to broadcast data to remote devices on a wireless network.